1. Field of the Invention
The present invention relates to an ultrasonic sealing apparatus for transversely sealing a tubular laminated packaging material filled with a content such as a liquid beverage, and more particularly to an ultrasonic sealing apparatus provided with an opposing jaw having a specified shape for improving sealability by controlling molten thermoplastic resin flow.
2. Description of the Related Art
Hitherto, as a packaging machine in which a packaging material web for a rectangular parallelepiped packaging container filled with juice, etc. is used by being sterilized, there has been known a filling and packaging machine shown in FIG. 1. In summary, the filling and packaging machine comprises a rewinder 2 supporting a laminated packaging material web 1 in a rolled state, a sterilization device 3 for sterilizing the plate-shaped laminated packaging material web successively rewound from the rewinder, a longitudinal sealing section 4 for sealing longitudinally both end portions of the sterilized laminated packaging material web an thereby forming a tubular laminated packaging material web, a liquid supply tube 5 for filling a fluid into the web formed in tubular form, a transverse sealing device 7 for transversely sealing the tubular laminated packaging material web in a direction perpendicular to the longitudinal direction thereof with a fluid while feeding downward a tube filled with the content by a length substantially corresponding to one package and, at the same time, continuously forming a pillow-shaped container 6 whose sectional shape is rectangle, and a shaping device for forming the pillow-shaped container 6 by folding its end portions into a rectangular parallelepiped container 8 which is a final form. And, the transversely sealing device 7 is composed of a sealing unit, a sealing jaw for fixing the sealing unit, and driving means for driving the sealing jaw.
Further, as the ultrasonic sealing apparatus, besides an ultrasonic sealing apparatus which comprises a piezoelectric driving unit having a piezoelectric ceramic plate or a magnetostriction driving unit, that is connected to an AC supply source, and a horn having an elongated sealing face, and which is characterized by further having one or more reaction bodies that together with the horn form a frequency of a half wavelength (Japanese Patent Laid-Open No. 2231/1995), there have been known many ultrasonic sealing apparatuses (Japanese Patent Publication No. 22784/1987, Japanese Patent Publication No. 2544450/1996, Japanese Patent Laid-Open No. 33121/1995, Japanese Patent Laid-Open No. 92046/1981, Japanese Patent Laid-Open No. 15741/1994, and the like).
Among these ultrasonic sealing apparatuses, there has been known an ultrasonic sealing apparatus for sealing openings at upper and lower ends of a formed cylindrical liquid container having an overlapping bonded portion approximately at a center of a container portion which includes a horn and an anvil, wherein a band-shaped ridge is provided nearly at a center of a face of the horn butting against a portion to be sealed, a concave groove perpendicular to the ridge is provided nearly at a center of a face of the anvil butting against the portion to be sealed, a bottom portion of the concave groove is made into a two-step structure and its step portion and both end portions are tapered, and an acute angle protruded slant face extending sideward is provided at an end portion of the center of the bottom portion (Japanese Utility Model Laid-Open No. 147108/1988, Registered Utility Model No. 3004786).
As shown in FIG. 2, a tubular laminated packaging material 11 filled with a content such as a liquid beverage is transversely ultrasonically sealed with a fluid by using a sealing jaw 10 consisting of a horn and an opposing jaw 20. The tubular laminated packaging material is pressed together and, as a result, a thickness of a longitudinally sealed three-ply portion 12 is larger than that of the remaining two-ply portion. The inventors of the present invention have discovered a problem in that steps are formed in the vicinity of both end portions of the longitudinally sealed portion. As a result of the steps, the sealing pressure becomes uneven so that a tunnel (through passage) occasionally occurs in the step portions, thereby generating a sealing failure.